Composite parts, such as those used in the manufacture of aircraft, can be constructed using various production methods, such as filament winding, tape placement, overbraid, chop fiber roving, coating, hand lay-up, or other composite processing techniques and curing processes. Most of these processes use a rigid cure tool/mandrel on which composite material is applied and then cured into a rigid composite part. For example, automated fiber placement (AFP) machines may be used to place fiber reinforcements on molds or mandrels to form composite layups. Following, composite parts may be cured within an autoclave that applies heat and pressure to the part during a cure cycle.
Some composite part geometries include internal cavities that may cause the part to collapse under application of composite material or autoclave pressure unless a tool such as an inflatable bladder is placed in the cavity. Such an inflatable bladder may be inflated during a cure process so as to react the autoclave pressure force applied to the part. Typically, these inflatable bladders are pressurized by venting them to the autoclave pressure through a vacuum bag.
However, during the automated fiber placement of the composite materials, the AFP machines exert pressure on the mold and bladder. Thus, existing inflatable bladders used in fabrication of composite material layups to inflate and provide even pressure during the cure cycle often deform due to the exerted pressure, which can impact laminate quality. Other solutions that use stiff bladders to maintain the internal cavity shape during the curing process typically only give a small improvement in deformation during fiber placement, but may not perform as well during the cure cycle.
Still other types of bladders have other drawbacks. Removable rigid bladder inserts can be used, but this requires a secondary installation and removal operation requiring additional labor and time. Solid mandrels can be used in place of bladders to provide resistance to deformation during fiber placement, but such mandrels are heavy and often do not provide even pressure during the cure cycle that reduces part quality. Shape memory polymers can also be used to change a state of bladder stiffness, however, this type of bladder is also typically heavier and very complex to design. Accordingly, there is a need for a bladder design that will allow the bladder to be rigid for automated fiber placement improving part quality, and also allow the bladder to be flexible during the curing cycle.